Facsimile system



Aug. 4, 1942'.

Vw. H. Buss FACSIMILE SYSTEM Filed Aug. 30, 1940 2 Sheets-Sheet 1 INV ENTOR. WARR H. BLISS BY )f Mfrolirlvznf.v

Aug. 4, 1942. w. H. Buss 2,292,099

Y f FACSQMILE SYSTEM Filed Aug. 50, 1940 2 Sheets-Sheet 2 1kg. 3R50e/VER U E ra 6R10 oF ,4L TUNE 36 TUBE 44 GENERATOR AND KEYER r M o g94 f 60 0 or -w72' ,6 l l AMPL/F/ER @AA/0 mss Mmmm AND F/LTER H0-RECT/F/ER 7'0 290- SCLLTOR INVENTOR.

1 VVAgEN H. BLISS BY wvl-W ATTORNEY.

Paenied Aug. 4, 1942 UNITED STATES4 PATENT OFFICE 11 claims. ,(cl. 17a-6.7)

This invention relates to facsimile and photoradio systems whereinsignals are transmitted from one location to another. the signals beingused to produce facsimile reproductions of the subject matter beingscanned at the transmitter.

More specifically, the present invention relates to apboto-radioreceiver for receiving phase modulated or phase displaced impulses andconverting the received impulses into voltage variations of a constantfrequency but of a variable length.

In previously used facsimile and photo-radio systems, the commonly knownconstant frequency variable dot system has been used in which thepicture signals as derived from the facsimile scanner areusedtokey atransmitter at a-predetermined and constant frequency in order to sendout signal impulses, the lengths of the individual impulses beingcontrolled in accordance with the strength of the signals derived fromthe scanner. These voltage variations of a constant frequency and of avariable length are then used to key a transmission frequency in orderthat the keyed signals may be received at a remotely located receiver.The received signals, therefore. vary in length and occur at apredetermined fixed frequency, the length of the impulses beingindicative of the light value of the subject being scanned, and thesevoltage variations are then used to control the amount of ink suppliedto the printing drum or the amount of pressure applied on the printing bar of a facsimile receiver in order to reproduce the particular imagebeing scanned at the transmitter.

Systems in which constant frequency variable dot transmission is used,for certain inherent objections, frequently prevent the production ofimageswith the desired clarity and fidelity. Normally, the carrierfrequency chosen for such work is relatively high, and, if the signalsarrive at the receiver over two or more paths which are dili'erent inlength. then the received signals will not have the desired length andthe image frequencies as lreceived will cause considerable distortion atthe receiver so that good high fidelity pictures cannot be reproduced.Furthermore, atmospheric disturbances frequently causefalse indicationsat the receiver or cause the length of the key carrier to be shortenedor increased so as to materially impair the fidelity of the reproducedpicture.

For these reasons systems known in the art have been developed forsending out the key impulses in phase displacement. the degree of phasedisplacement being determined by the light intensity of the picturescanned. In the constant frequency variable dot sysiem, the intelligenceof the received signals resides in the length of the dot or the lengthof each successive impulse, whereas in the phase displacement system theimpulses arrive at a predetermined fixed frequency, but their phaserelationship of arrival as compared to the fixed frequency is varied inaccordance with the light values of the picture, and accordingly, theintelligenceof the received signals is contained in the degree of phasedisplacement.

Such systems are particularly desirable since the length of the variouskeyed impulses is not controlling at the receiver, and accordingly, if

two or more paths are traversed by the transmitted Wave, then thereceiver is unaiected by impulses arriving after the ilrst impulse, andfurthermore, atmospheric disturbances do not affect the receiver sincechanges in the lengths of the keyed impulses have no eil'ect on thereceiver. The receiver responds only to the phase displacement of theimpulses as compared to a fixed standard, and such phase displacement asdetermined by the light value of the scanned p'icture is unaffected bymultiple path reception or atmospheric disturbances.

The present invention relates to a receiving system Vfor receivingimpulses which are phase displaced in accordance with the subject mattertransmitted, and for converting the impulses as received into impulsesof a constant frequency and variable length, or constant frequency vari-I able dot. These converted constant frequency variable dot impulses arethen used at the printer for reproducing the picture.

It is therefore one purpose of the present invention to provide afacsimile or photo-radio receiver for converting phase displacedimpulses of a constant frequency into voltage variations of a constantfrequency and variable length.

Another advantage of the present invention resides in the provision ofmeans for synchronizing the receivers with the transmitter.

Stili another advantage of the present invention resides in theproduction of a facsimile or photo-radio receiver which is maintained insynchronlsm with the transmitter through the use of a series ofsynchronizing impulses sent at a frequency of substantially double thefrequency of the impulse transmission.

A further purpose of the present invention resides in the production ofa facsimile or photoradio receiver in which phase displaced impulses ofa predetermined frequency may be converted into voltage variations of apredetermined fre- Figure 1 shows one form of the present inVA vention;A

Figure 2 shows a series of curves indicating wave form, phasedisplacement a d impulse length at various points in the receiwersystem, and

Figure 3 shows a modified form of the present invention.

vIn Figure 1 is shown an antenna I0 for receiving the phase displacedimpulses from a transmitting system. Attached to the antenna is areceiver I2 which may include one or more stages of amplification, and ademodulator. The

type of receiver used is not important, since either a tuned radiofrequency or superheterodyne circuit may be used. The output from thereceiver is supplied to a tone generator and keyer I4 wherein a tonefrequency of several thousand cycles per second is generated, the tonefrequency being keyed in accordance with the demodulated signal output.of the receiver I2. The output of the keyer I4 is supplied to anamplifier and rectifier I6 which againA may be of any desired design.The amplifier at I6 is included in the figure inasmuch as the spacingbetween the tone generator and keyer I4 and the amplifier and rectifierI6 may be some considerable distance, since it is often desirable toactually receive the signals at one point and to produce the facsimileor photo-radio images at another point. If the keyer I4 and therectifier IIi are located in relatively close proximity, then theaddition of the amplifier after the keyer and before the rectifier isnot necessary.

In order to clearly describe the operationof the present invention,various curves indicating voltage variations are shown in Figure 2.Referring to this figure, a light wedge 2I is shown, which varies inlight value from white to black. The curves of the figure are associatedwith the lightwedge and the variation in impulse phase displacement orlength in the various parts of the system is indicated in the drawingsso that these variations may be compared with the corresponding lightvalue of the light wedge. The curve 22 shows a series of impulses ofconstant frequency which are displaced in phase relationship so far astheir beginning is concerned with respect to a standard frequency shownat 21 in the figure. When the light value of the image is high, then thephase displacement, as indicated by Figure 2, is at a minimum, whereaswhen the light value of the picture is dark, or low, then the phasedisplacement of the transmitted impulses is. at a maximum. Actuallythese impulses are keyed impulses of a high frequency carrier, the highfrequency carrier not being shown in the figure. These impulses may notcontinue throughout their allotted time in accordance with the lightvalues of the image by reason of atmospheric conditions, or, `as amatter of fact, the impulses may be increased in length fory the samereason. Because of the design of thepresent invention, the terminationof the .impulses shown at 22 is not indicative,

and only thepha'sel displacement between these' impulses as c Jrnparedto the fixed frequency 21 are controlling as will be shown later. Theimpulses 22 are, of course, received by the receiver I2, and, afterdemodulation, are used to key the tone generator I4 so that a series ofimpulses of tone frequency will be produced by the tone generator andkeyer, this series of impulses being indicated at 23 in Figure 2. Thetone frequency is materially less than the carrier frequency 'used inthe actual transmission. In view of the design of the tone generator andkeyer,

the tone oscillations 23 are of constant frequency and amplitude butvary in phase displacement in accordance with the received signals andthe length of the tone impulses 23, although not controlling in thereceiver, are in fact determined by the length of time that the receivedimpulses 22 persist due to multipath transmission.

These keyed tone impulses are then supplied to the amplifier andrectifier I6 to produce at the output thereof a series of impulses 24which are also'phase displaced with respect to the fixed frequency 21and which vary in length in accordance with the length of the keyed toneimpulses as supplied by the keyer I4. The .displacement of the beginningof the impulses -24 from the,

fixed'frequency 21 is an indication vof the subject matter transmitted.The impulses 24 do not generally terminate in phase with the fixedfrequency 21; however, this is not vital since the receiver responds tothe phase displacement.

The rectified output of the amplifier and rectiiier I6 of Figure 1 asshown by the curve 24 in Figure 2 is supplied to the control electrode3l of a gas-filled discharge tube 30. The discharge tube may be of thetype 885 tube and includes a cathode, a control electrode and an anode.This tube is rendered conductive by the application of a positiveimpulse to the control electrode, but in view of the fact that the tubeis gas-filled, conduction will continue even though the controlelectrode is made negative and the tube can be rendered non-conductiveby removal or suppression of the anode potential below a potentialsuiiicient to maintain a discharge from the cathode to the anode. Thecathode of the discharge tube 3l! is connected to ground byway ofcathode load resistances 32 and 34, the latter of which is preferablymade in the form of a potentiometer. rectifier i6 and the gas-filleddischarge tube 30 is by way of the coupling condenser 36, and arelatively large resistance 38 is included in series with the controlelectrode of tube 30 in order to limit the current in this electrode toa safe value. The control electrode 3| is connected to a point along thepotentiometer 34 by resistance 40. The anode of the gas-filled tube 30is maintained positive by a connection to a positive source of potentialthrough the anode resistance d2.

Anotherv gas-filled discharge tube 44 is also used which is similar tothe tubeV 30 and which also includes a cathode, a control electrode andan anode. The cathode of tube 44 is connected to ground through cathodeload resistances 46 and 48, the latter of which is preferably made inthe form of a potentiometer., The control electrode of the gas-filledtube 44 is connected to a point along the potentiometer 48 by a gridresistance 50 and the primary winding 52 of the transformer 53. Theanode is maintained positive with respect to the cathode by a source ofpositive potential, the source being connected to the anode through ananode resistor 58. 'I'he Coupling between the two anodes of thegas-nlled discharge tubes 3l and 4I are inter-connected by a condenserIl.

A synchronous oscillator 60 is provided which generates voltagevariations of substantially sinusoidal wave form and of a frequencyequal to the frequency used in transmitting the phase displaced signalimpulses. The oscillator 6l is synchronized by means of the impulsesreceived from the transmitter, these impulses being supplied to theoscillator I by way oi' conductor I2 when the movable armature 64, whichis associated with the electromagnet I8, is in its lower position. Atthe transmitting apparatus, the subject matter to be transmitted byfacsimile or photo-radio is scanned in the usual manner employing arotary drum and a scanning head, and

between each scanned line impulses are transmitted corresponding toblack or white, and these impulses between each scanned line are usedfor synchronizing purposes. At the receiving apparatus a rotating drum1li is used to which is connected ai motor 12 for rotating the drum.Mounted on the shaft of the drum is a cam wheel 14 cooperating withwhich are a pair of contacts 16. For each revolution of the drum thecontacts are closed for a relatively short space of time, and throughthe energy supplied by the battery 18 the coil 68 of lthe electromagnetis energized to move the armature 64 from the upper to the lowerposition, thus directing the rectified impulses from the rectifier I6 tothe oscillator 60.

The motor 12 may be supplied with energy from a power line and may alsobe supplied with the oscillations from the oscillator 60 inorder tomaintain the proper synchronous operation of the motor. Once therotating drum 1B has been properly phased with respect to thetransmitter, such synchronous operation of the proper phase relationshipis maintained by reason of the connection of the motor-12 to theoscillator 60. Furthermore, the oscillator is maintained in propersynchronous operation with the transmitter by supplying to theoscillator a series of synchronizing impulses between each scanned lineeach time the relay winding 88 is energized. When the relay winding 63is deenergized, the rectifying energy from the rectifier I6 is suppliedto the I control electrode 3l of the gas discharge tube 2l.

As stated above, the synchronous oscillator Bl! supplies voltagevariations of substantially sinusoidal wave form as indicated in thecurve 25 in Figure 2 and these voltage variations are applied to theprimary winding il of the transformer 53. These voltage variations areaccordingly impressed upon the control electrode of the gas dischargetube M.

Associated with the curve 26 in Figure 2 is a dotted line 28 whichindicates the potential at which the gas discharge tube Il is renderedconducting. When the voltage variations exceed a voltage valuerepresented by the dotted line 28, then the tube 44 is permitted toconduct and such conduction will continue until the difference ofpotential between the anode and the cathode of the tube is materiallyreduced even though the potential of the control electrode may actuallysubsequently be reduced due to the variation of the voltage as shown at26 in Figure 2.

The voltage variation of sinusoidal wave form as indicated at 25 inFigure 2, as stated above, is produced by the oscillator 80 in responseto the synchronizing signals received from the transmitter. Thesesynchronizing signals bear a fixed phase relationship to the constantfrequency imtube 44 in phase with the fixed `frequency 21 u,

indicated in Figure 2.

Normally, the discharge tube M is conducting and such conductioncontinues until a rectiiled impulse is supplied to the control electrode3l of tube III from the rectifier I6. The front oi' this impulse fromthe rectifier I6 is phase displaced from the standard frequency 21 by anamount depending upon the light value of the picture being scanned atthat particular instant. The leading edge of the impulse drives thecontrol electrode 3l positive to cause the tube 30 to become conducting.and, in view of the accompanying potential drop at the anode of tube 3B,causes a substantial and sudden decrease in the potential betwen thecathode and anode of gas discharge tube M because of the presence ofcondenser 58. Tube 44 is therefore rendered nonconductive and thisnon-conductive condition continues until the voltage applied to thecontrol electrode of tube M reaches a value corresponding to thepotential represented by the dotted line 28. At this time tube 4I isrendered conductive, and conversely, tube 3|! is rendered nonconduotive.The two tubes 30 and 44, therefore, operate alternately, and tube 30 isconductive for a time period represented by the phase displacement ofthe received impulses rectified by the rectifier I6 (as represented at24 in Figure 2) as compared to the fixed frequency standard replresented at 21 in Figure 2. j,Tube 3B will remain conductive until tube44 is made conductive by the voltage variation 25 as supplied by theoscillator 60, even though the rectified impulse 24, as supplied to thecontrol electrode of tube Ill, ceases to be present.

During the time when tube 30 is rendered conductive, a predeterminedvoltage drop is present across the cathode resistor 32. 'I'his voltagevariation is represented at 25 in Figure 2, and it will be noticed thatthe frequency of occurrence of these voltage variations is constant andcorresponds to the transmission frequency, but that the impulses are ofvarying length, depending upon the phase displacement of the transmittedimpulses. Therefore, the voltage variations which are derived from theresistance 32, are in fact voltage variations of constant frequency andof a variable length, depending upon the light intensity of thetransmitted subject matter. The portion of the invention as thus fardescribed operates to convert constant frequency phase displacedimpulses into constant frequency variable dot impulses.

The voltage variations appearing across the resistance 32 are applied tothe control electrode of an amplifier tube 30 having a cathode, acontrol electrode and an anode. The cathode `is connected to thenegative terminal of a source of potential, and the anode is connectedto the positive terminal of a source of potential through a loadresistance 82. Furthermore, the control electrode is connected to groundby way of resistance Ill, and the cathode end of resistance 32 isconnected to the control electrode of tube Il by way of resistance 8l.Across the resistance V 82 appears a voltage variation similar in waveform to the voltage variations shown at 26 in Figure 2 but of increasedamplitude and of an amplitude suiiicient to cause the operation of theglow discharge tube Sil. The glow discharge tube Btl is connectedacrosstthe resistance 82 in series with a resistance te. The glowdischarge tube lift as well as its associated optical system 88 aremoved axially along the recording frame by means of a worm drivemechanism gli which is mechanically connected to the recording drum l@by way of gears @2. The gear ratio of the gears il@ as well as the pitchof the worm drive 9@ depend upon the number or lines scanned per inch cisubject matter.

From the above, therei'cre, it may be seen that there has been provideda very simple arrangement for converting phase displaced voltagevariations into voltage variations of a constant frequencyY variablelength, 4the latter voltage variations being used as the recording meansfor reproducing the scanned image. The disadvantages' of using constantfrequency phase displaced impulses in the transmission from thetransmitter to the receiver have been outlined above, and from the aboveexplanation oi the applicants receiver system, it may be readilyappreciated that transmission over multiple paths or in atmosphericdisturbances will not affect the fidelity of the picture reproduced atthe receiver, since the length of the converted impulses depends solelyupon the phase displace A"modication of the present invention is shownin Figure 3, in which a different type of 4Q synchronizing apparatus isused. If the device disclosed in Figure l'is to be operated at arelatively rapid rate, then some difficulty may be experienced inproducing arelay which will respond at a sumciently rapid rate totransfer the rectified synchronizing and picture impulses from therectifier I6 to the synchronized oscillator G0 and to the controlelectrode of gas discharge tube 30. In Figure 3 this element has beenomitted, and the apparatus shown in Figure 3 is intended to be used witha transmitter wherein the synchronizing impulses are sent tov thereceiver at a rate double the frequency used in transmitting the phasedisplaced impulses.` If the phase displaced impulses are sent at afrequency of 100 cycles per second, for example,

then the synchronizing impulses between each f scanned line would be'transmitted at a constant! phase relationship and at a frequency of 200i cycles per second. In this case, the rectified output from Itherectifier I6 is supplied directly to the control electrode 3| of gasdischarge tube and the rectified output is also supplied to a bandI passfilter which is designed to pass all frequencies between substantially110 cycles and 290 cycles per second. It is not desired that the bandpass filter pass frequencies of the order of 100 cycles per second ifthis is the frequency used for transmission of the picture signals, andfurthermore, it is not desired that the band pass filter pass 300 cyclesper second since the third harmonic of the picture frequency would thenbe transmittedto the synchronized oscillator. Since the synchronizingimpulses of a frequency of 200 cycles per second, for example, aretransmitted only between successive line scannings, then, during thetransmission of such synchronizing signals the band pass lter willsupply the synchronizing signals to the oscillator 60 which in turnsupplies the controlling impulses to the motor 12 in order to maintainproper synchronous operation of the motor and also supply voltagevariations to the control electrode of tube dll.

As stated above, these voltage variations for controlling the tube Mlmay be of sinusoidal wave form as shown. at 25 in Figure 2, but as amatter of fact any desired wave 'form may be used so long as its phaserelationship with respect to the fixed standard frequency 2l is suchthat the tube lil is caused to become conductive in phase with thestandard frequency The gas discharge tubes 3@ and ltl, as well as theremainder of the system and the recording drum are not shown in Figure3, since they are identical to the elements shown in Figure i, Ey usingthe circuits shown in Figure 3 it is possible to eliminate the use ofthe relay winding du and the vibrating armature @t so that relativelyhigh frequencies and transmission rates may be used.

Although in describing Figure 3 a transmission frequency of l00- cyclesper second is suggested, itis to be understood that other frequenciesabove or below cycles per second could as Well be used.

Either the circuit shown in Figure lor the circuit shown in Figure 3 maybe used with the oscillator where the signal impulses are transmitted inphase displacement with respect to a fixed standard frequency, thedegree of displacement being determined in accordance with the lightvalues of the subject matter being scanned. Furthermore, both systemswill convert the constant frequency variable phase impulses intoconstant frequency variable length impulses which may be used on arecording drum and both systems will maintain the recording drum inproper synchronous operation with thev transmitter. It is possible todesign oscillators which are sufficiently stable in operation tomaintain the desired' synchronous `operation during the time requiredfor the scanning of one line, and it has been found that synchronizingtheoscillator during the interval between each line scanned is entirelysufficient. f

Various alterations and modifications may be made in the presentinvention without departing from the spirit and scope thereof, and it isdesired that any and all such modifications be considered within thepurview of the present invention except as limited by the hereinafterappended claims.

I claim:

1. A receiving system wherein is received a carrier modulated bysignalling impulses at a predetermined frequency, said impulses beingdisplaced in phase relationship with respect to their frequency ofoccurrence in accordance with the 'intelligence to be transmitted,including means to demodulate the received carrier to produce a seriesof impulses of the predetermined frequency, the beginning of each.impulse being phase displaced with respect to a xed reference frequencyin accordance with the phasedisplacement of the received impulses, meansfor generating a xed reference frequency, and means responsive to thephase displacement of the produced impulses with respect to thevgenerated fixed reference frequency for producing control impulses of aconstant frequency and of a variable length,

the length of the control impulses being deterv mined by the degree ofphase displacement.

said impulses being displaced in phase relationship with respect to afixed reference frequency in accordance with the intelligence to betransmitted, including means to demodulate the received carrier toproduce a series of control impulses occurring at the predeterminedfrequency, the beginning of each impulse being phase displaced withrespect to a fixed reference frequency in accordance with the phasedisplacement of the received'impulses, means for generating a fixedreference frequency, means responsive to the phase displacement of thecontrol impuses with respect to the generated fixed frequency forproducing recording impulses of a substantially constant frequency andamplitude but of a variable length, the length of the recording impulsesbeing determined by the degree of phase displacement, and meansresponsive to the constant frequency variable length recording impulsesto produce a recording.

3. A receiving system wherein is received a carrier modulated bysignalling impulses occurring at a predetermined frequency, saidimpulses being phase displaced with respect to their frequency ofoccurrence in accordance with Athe intelligence to be transmitted,including means to demodulate the received carrier to produce a seriescf impuses of the predetermined frequency, the beginning of each impulsebeing phase displaced with respect to a fixed reference frequency inaccordance with the phase displacement of the receivedimpulses, meansfor generating a fixed reference, frequency, and means responsive to thephase displacement of the beginning of each produced impulse withrespect to the fixed reference frequency for producing control impulsesof a substantially constant frequency and amplitude but of a variabletime duration, the time duration of the control impulses beingdetermined by the degree of phase displacement with respect to the fixedreference frequency.

4. A facsimile receiving system wherein a carrier is received, thecarrier being modulated atl intervals of a constant frequency and at asubstantially constant amplitude, the phase displacement of themodulation intervals being variable in accordance with the subjectmatter transmitted with respect to a fixed referencefrequency, includingmeans to demodulate the carrier to produce a series of impulses ofsubstantially uniform intensity and of substantially constant frequencybut having a phase displacement with respect to la xed referencefrequency in accordance with the received modulation intervals and thesubject matter transmitted, means at the receiver to generate a fixedreference frequency, and means to compare the phase relationship of theproduced series of impulses and the generated xed reference frequency toproduce control impulses of constant frequency and amplitude but of alength depending upon erence frequency in accordance with the subjectmatter transmitted, including means to demodulate the carrier to producea series of signal impulses of substantially uniform intensit and ofsubstantially constant frequency with the beginning of each signalimpulse phase displaced with respect to a fixed reference frequency inaccordance with the received modulation intervals, means at the receiverto generate a fixedV reference frequency, and means responsive to thephase displacement of the produced signal impulses with respect to thegenerated fixed reference frequency to produce impulses of constantfrequency and amplitude but of a time dunation depending upon the degreeof phase displacement.

6. A facsimile receiving system wherein a carrier is received, thecarrier being modulated at intervals of a constant frequency and at asubstantially constant amplitude, the phase displacement of themodulation intervals being variable in accordance with the subjectmatter l transmitted including means to demodulate the carrier toproduce a series of signal impulses of substantially uniform intensityand of substantially constant frequency, said produced series ofimpulses .having a phase displacement with respect to a fixed referencefrequency in accordance with the subject matter transmitted asdetermined by the'received modulation intervals, means at the receiverto generate a fixed reference frequency, means to compare the phaserelationship of the produced series of signal impulses and the generatedfixed referencefrequency to produce control impulses of constantfrequency and amplitude but having a length depending upon the degree ofphase displacement ofthe signal impulses with respect to the fixedreference frequency, and means responsive to the produced controlimpulses.

'7. A facsimile receiver wherein phase modulated impulses of apredetermined substantially constant frequency are received includingmeans for generating a fixed reference frequency corresponding to thefrequency of the received impulses, and means including an electronicdischarge device responsive to the phase displacement of the receivedimpulses with respect to the generated fixed reference frequency forproducing a series of impulses of substantially constant amplitude andof the same frequency as the received impulses but of a durationdepending upon the phase displacement of the received.

impulses.

8. A facsimile receiver wherein phase modulated impulses of apredetermined frequency are y received including means for generating afixed the phase dispacement of the produced series reference frequencycorresponding to the frequency of the received impulses, meansresponsive to the phase displacement of the received impulses withrespect to the generated fixed reference frequency for producing aseries of impulses of substantially constant amplitude and of the samefrequency but of a duration depending upon the phase displacement of thephase modulated received impulses, said means including a pair ofelectronic discharge tubes, and means for rendering the tubesalternately conductive, one of said discharge tubes responding to thereceived phase modulated impulses and the other of said discharge tubesresponding to the generated fixed reference frequency.

9. A facsimile receiver wherein are received phase displaced impulses ofa predetermined frequency in accordance with the intelligence to betransmitted including means for generating a xed reference frequencycorresponding to a multiple of the frequency of the received impulses,and means responsive to the phase displacement of the received impulseswith respect to the fixed reference frequency for producing a series ofimpulses of substantially constant amplitude and of the same frequencybut of a length depending upon the degree of phase displacement of thereceived impulses, said means including a pair of alternately conductingdischarge paths, one of said discharge paths responding to the beginningreceived phase displaced irnpulses and the other of said discharge pathsresponding to the generated fixed reference frequency.

l0. A facsimile receiving system wherein a modulated carrier isreceived, the carrier being modulated by a series of impulses occurringat a predetermined frequency, the modulating impulses being phase'displaced with respect to a lxed reference frequency by an amountdepending upon the subject matter to be transmitted, means to demodulatethe vcarrier frequency to produce a series of signal impulses of thepredetermined frequency, the beginning of each impulse being phasedisplaced with respect to a iixed reference frequency in accordance withthe received phase displaced impulses, means to generate a xed referencefrequency corresponding to the frequency of the produced signalirnpulses, and means. responsive to the phase displacement of theproduced signal impulses with respect to the generated iixed referencefrequency for producing aseries of impulses of similar irequency and ofsubstantially constant amplitude but of a duration depending upon thedegree of phase displacement.

11.,.A facsimile receiving system wherein a modulated carrier isreceived, the carrier being modulated by a series of impulses occurringat a predetermined frequency, the modulating impulses being phasedisplaced With respect to a xed reference frequency by an amountdepending upon the subject matter to be transmitted, means tc demodulatethe carrier frequency to produce a series of signal impulses of thepredetermined irequency, the beginning of each ime pulse being phasedisplaced with respect to a iixed reference frequency in accordance withthe phase displacement of the received impulses, means .to generate afixed reference frequency corresponding to the frequency of the producedsignal impulses, means responsive to the phase displacement of theproduced signal impulses with respect to the generated xed referencefrequency for producing a series ci impulses of similar frequency and ofsubstantially constant arnplitude but oi a length depending upon the degree of phase displacement, said means including a pair of electronicdischarge paths which are rendered alternately conductive, one of saiddischarge paths responding to the beginning of each produced impulse andthe other of said discharge paths responding to the generated xedreference frequency, and means responsive to the produced constantfrequency variable length im pulses for producing a facsimile recording.

A WARREN H. BLISS.

